How to quickly create duplicate recessed portion?
I guess there are at least 2 ways of doing it: either you do it &quot;for real&quot; with topology, or you simulate it in the material with Bump or Normal maps
Topology:

Create a cylinder with as many vertices as you want
Select the face loop
Select &gt; Checker Deselect so that only one of two faces is selected
Keep the faces selected and Alt+E &gt; Extrude &gt; Individual Faces
Scale down these extrusions except on the Z axis with S and Shift+Z

Material:

Create a surface with a series of crenels
Bake this surface so that you have a Normal image
Use this Normal for you whole ring
(on my screenshot it's very quick made, sorry)